2. "When re-pitching, we just add fresh wort to the carboys"...you are over pitching the others.

+1 to that. Tubercle hit the noodle on the head with that one.

Definitely agree with this as well. Yeast growth during fermentation means that you'll have significantly more yeast for the second batch, and unless it's a very high gravity beer you won't need all of it.

If your FG is 1.013 even when overpitching, I'd look at your recipe or your mash temperature to try to make a more fermentable beer. Calibrate your thermometer against a lab grade model or quality certified digital thermometer to make sure you are mashing at the temperature you think you are.